Apparatus for producing alternating current



Sept. 19', 1961 Filed Jan. 5, 1959 Lig/'if l.. J. JOHNSON 3,001,124

APPARATUS FOR PRODUCING ALTERNATING CURRENT 5 Sheets-Sheet 1 Sept. 19,1961 L. J. JOHNSON APPARATUS FOR PRODUCING ALTERNATING CURRENT FiledJan. 5, 1959 3 Sheets-Sheet 2 BY Z Sept. 19, 1961 L. J. JoHNsoN3,001,124

APPARATUS FOR PRODUCING ALTERNATING CURRENT Filed Jan. 5. 1959 ssheets-sheet :s

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E@ f" Tg1-@M541 United States Patent O M 3,001,124 PRODUCING ALTERNATINGg CURRENT Leopold J. Johnson, Anaheim, Calif., assignor to The ,SieglerCorporation, Anaheim, Calif., a corporation of Delaware Filed Jan. 5,1959, Ser. No. 785,041 11 Claims. (Cl. S22-61) APPARATUS ron to use ahigh speed turbine, -i.e., steam or gas turbine,4

as a prime mover for driving the generator due to the low operating costor small size of such turbines. lt

has been necessary in the past to provide some type of speed reducingcoupling between the turbine and the generator where an alternatingcurrent of relatively lowy frequency, eg., 60 cycles, is desired. |Forexample, where the shaft speed of a turbine is of the order of 10,000r.p.m. it is necessary toprovide a speed reducing coupling such as agear train which provides a reduction ratio of the order of 3 to 1 todrive a two-pole alternator and produce a 60-cycle output signal. Suchcouplings are very expensive. Furthermore, to accurately control theoutput frequency of the alternator, it has been necessary in the past tocontrol the shaft speed of the alternator since the shaft speed of theturbine will vary` to some eXtent.` Arrangements for controlling thespeed of `rotation of alternators are complex, cumbersome; slow actingand expensive. l

The above difficulties are overcome by the present invention bycontrolling the magnetic field for the Varmature of a generator inVaccordancewith Van alternating" current reference signal. TheV apparatusof this invention includes .a generator having an armature and at leastone field windingv for producing a magneticfield for the armature, meansfor driving the generator and means for applying `an alternating currentreference signal to the field winding for controlling the amplitude anddirection of the magnetic field in accordance with Y thereference signalto cause the armature to'produce an alternating current output inY theform of a modulatedv wave, the frequencyY of the modulated wave -beingpro-v portional to the speed of the driving means, and the frequency ofthe modulating wave being equal to the` frequency of the'r referencesignal. The apparatus of this invention further includes means coupledto the'4 armature for demodulatingthe armature `output to provide analternating current output signalhaving a frequency equal-tothereference signal. Thus the present invention providesa novel apparatusfor producing alternating current in substantial ramounts and having a`con trolled frequency.

The invention will be explained in more detail in reference to theaccompanying drawings in which: A

FIG. 1 isa block diagram of one embodiment of the present invention;

FIG. 2-.is a perspective AView of a simple. type of gen-i erator andswitching-'means that maybe employed in the apparatus of FIG. 1; `f

FIG. 3 is Ya graph illustratingV waveforms taken at various points inthe apparatus of FIGS. 1 and Y2 where'-` in the` ordinate representsvoltage land the abscissa represents time; f f

' FIG. 4 is a schematic circuit diagram," partiallyiin- Patented Sept.19, 1961 ICC 2 block form, illustrating another embodiment of thisinvention;

lFIG. 5 is a schematic circuit diagram, partially in block form,illustrating a further embodiment of this invention;

FIG. 6 is a graph similar to the graph of FIG. 3 illustrating waveformstaken at Various points in the circuit of IFIG. 5;

FIG. 7 is a schematic circuit diagram, partially in block form,illustrating another embodiment of this invention;

FIG. 8 is a simplified illustration of a field winding arrangement for agenerator that may be employed in the apparatus of this invention; and

FIG. 9 is a schematic circuit diagram of a diode demodulator that may beemployed in the apparatus of this invention.

Referring now to the drawings and more particularly to FIG. 1 thereof, agenerator :10 includes an armature 12 for producing an alternatingcurrent and a field winding 14 for producing a magnetic eld for thearmature 1'2. A prime mover 16 is coupled to the generator 10 fordriving the generator at any desired speed. For example, the prime mover16 may be a gas turbine having a shaft revolution of the order of 10,000r.p.m. The reference signal generator 18 is coupled to the field winding14 to apply an alternating current of a predetermined frequency, Le., 60c.p.s. thereto to control the magnitude and direction of the magneticfield in accordance with the reference signal. netic field for thearmature the armature produces an output in the form of a modulated wavethat changes phase when the reference signal changes polarity. Thefrequency of the modulated wave is proportional to the Speed of rotationof the armature or driving means and the frequency of the modulatingwave is equal to the frequency of the Areference signal as will be morefully described. A pair of output terminals 20 is provided for derivingan alternating current output from the gen erator 10. A switching means21 under the.control `of the prime mover 16 is coupled between thearmature l2 and the output terminals 20 for alternately switching thearmature output across the output terminals 20` at a rate proportionalto speed of rotation of the armature to demodulate the armature outputand produce an alter- Y nating current output signal having a frequencyequal to l kthe frequency of the reference signal across the output'terminals 20.

Referring now to FIG. 2, a simplified generator is illustrated asincluding a pair of oppositely disposed poles 22 on which is wound thefield winding 14 to producen a magneticy field for the armature 12. Thearmature in this simplified illustration is disclosed as including onlyone coil 24 which is rotated within the magnetic field produced by thefield winding 14 and the poles 22. The

switching means 21 in IFIG. 2 includes two commutating -segments 26 and20 which are connected to opposite ends of the armature coil 24 by leads30. A pair of brushes 32 is coupled between the output terminals 20V andthe commutating segments 2.6 and 28.r In operation the reference signalgenerator .18 applies an alternating current signal such as thesinusoidal signal eR (shown in FIG. 3) to the field winding 14 to causethe field wind-Y ing 14 and the poles 22 to produce a sinusoidalmagnetic field for the armature 12. This causes the armature i12 toproduce an output Wave eA (shown in lFIG. 3) which varies in amplitudeand phase in accordance with the quency proportional to the speed ofrotation of thev armature and the number of poles in the generator.

By providing an alternating mag-` The waveform eA is a combinationV Thismodulated wave-which may be compared to a high frequency carrier signalresults from the relative rotation of the armature .12 with respecttothe poles 22. This modulatedwave 40 changesV polarity during eachrevolution of the armature 12, as shown. tThe 'amplitude of thismodulated wave 40 is controlled by the field strength which is in turncontrolled by the amplitude of the signal applied to the field winding14. When the reference signal eR changes polarity with respect to thefield winding 1-4V at times t1, as shown in FIG. 3, the phase of thearmature output eA also changes. Thus the armature output is similar toa modulated double side band suppressed carrier wave.

The switching means 21 demodulates the armature output `eA byalternately reversing the connection between the armature and .theoutput terminals 20. As sho-wn in FIG. 2, this connection is reversedonce during each revolution of the armature 12. Y This action isidentical to the commutator. action of `Vall() generator having only onecoil in the armature. The polarity of the output signal e changes attime t1 or when the phase of the armature output changes. Thus theoutput e0 is a sinusoidal wave having Aa frequency equal to thefrequency of the reference signal. The modulated wave 40 must o-f coursehave =a relatively high frequency with respect to the modulating orreference signal to provide a sinusoidal output across the terminals 20.v

As is shown in FIG.'3, the output voltage e0 contains a high frequencyripple component 44 which may be removed by a suitable filter ifdesired. This .ripple component in the -output due to the highfrequency-wave 40 may be substantially omitted by employing many coilsin the armature 12 and connecting the coils in the armature output sothat the resultant current is the sum of the voltages generated inseveral individual coils. While the switching means illustrated in FIG.2 includes a commutator khaving two segments, the number of segmentswill of course depend -upon the number'of poles employed in thegenerator."v Where four poles are employed a four-v segment commutatoris necessary, etc.

Referring now to` FIG. 4, there is shown another embodiment of theinvention in which a direct currentl (DC.) generator 50 is utilized. Thegenerator 50A includes' a field winding y52 which is connected to thereference signal generator 18,` an armature (not-shown) includes a iieldwinding 14 and an armature 12. A ref-v having a multiple coil winding,the ends of which are connected to a multiple segment commutator 53, anda pairl of brushes `54 coupled between' the commutator and the outputterminals 20. As is well known, the alternating -current produced in thearmature of a D.C. gener-- ator when a direct current is applied to theiield winding i thereof is rectified by the commutator and brusharrangement to produce av direct current output signal. In thek presentinvention an alternating current signalis applied g tothe i'eldgwindingof the D.C. generator 50 to cause the armature to produce a modulatedwave similar to that disclosed by the curve eA in FIG. 3. This modulatedwave or armature output is demodulated by the commutator to produce analternating current output signal 'across the output terminals 20 havinga frequency equal to the frequency of the reference signal. The outputsignal from the D.C. -generator contains substantially no rip-A plecomponent.

' VIn FIG. 5 a' further embodiment of the present inventionis shownwherein a single phase alternator 60 is coupled to a Vprime mover 16 tobe driven thereby and erence signal generator 18 is coupled to the iieldwinding 14'to cause the armature 12 tofproduce a modulated output waveeA (as shown 'in FIG. 6) in a manner similark tothat Adescribed withrespect to the apparatus of FIG. 2..

A-'full wave phase sensitive transistor demodulator62 is coupled betweenthe output terminals 20 and the armature 12 to demodulate the armatureoutput, as will 'be erence signal.

of powerY input terminals 63 which are connected to.k the armature 12and six control input terminals 64 which are connected to a tachometer65. The tachometer 65 is coupled to the shaft of the prime mover 16 forsensing the speed of rotation of the armature 12 andV to pro` vide fourseparate controlv signals ec, each having a frequency which is equal tothe frequency of the modulated signal `4t?. The armature output isdirectly connected to emitter electrodes of the transistors 67 and69,'as shown.` The tachometer 65 includes fourl separate windings V65A,f

65B, 65C, 65D, which are wound as shown by theconventional polaritymarkings. The windings 65A, 65B, 65C and 65D are connected between theemitter andbase electrodes of the transistors 66, 67, 68 and 69respectively. Current limiting resistors 70-73 are connected in seriesAwith the basel electrodes of the respective transistors to limit thecurrent therethrough.

As shown in FIG. 5, the windings 65A through 65D are connected to thebase and emitter electrodes of the transistors 66-69 so that only two ofthe transistors will be rendered conducting at one time.

between the emitter and base electrodes of thetransistors 66 and 69which renders these transistors conducting.V

At this Vsame time a negative signal is applied between the emitter andbase electrodes of the transistors 67 and 68= which maintains thesetransistors in a nonconducting state. When a negative control signal isgenerated in the tachometer windings thetransistors 67 and 68are'rendered'A conducting and the transistors 66 and 69 are renderedynonconducting. To provide full wave operation of the demodulator 62,windings 65A Vthrough 65D of the tachometer 65 are arranged to provide acontrol signal having a voltage amplitude larger than the'maximumamplitude of thevoltage developed in the armature 12.V

Thus 'current may flow in either direction through the transistors66-69, that is, from the emitter tothe collector or from the collectorto the emitter electrodes. WhenY a positive signal is generated in thearmature 12 and in` the .tachometer windings to renderY the transistors66 and` 69 conducting, a positive signal is applied'across'the outputterminals 20 and across a load 74 connected thereto.` Also when anegative signalis generated in the armaturey 12 and in the tachometerwindings to render the transistors 67 and 68 conducting a positivesignal is applied across the output terminals. This occurs when themoduwhen a negative voltage vis generated in the armature 12,

thereby producing `a negative voltage across the output` terminals 20,as shown by the curve eo in FIG..6. While the voltage produced by thelwindings of thek tachometer.

65 must be greater .than the voltages generated in the armature 12 toprovide full wave operation, little power need be supplied by thetachometer windings 65A through 65D since these windings are controllingthe base emitter electrodes of the transistors 66 through 69. Manyothertypes of demodulators may be employed in the circuit of FIG. 5 insteadof the transistor demodulator 62A for demodulating the armature output*to providean alternating current signal across the output terminals V20whichhas :a frequency equal to the frequency of the ref-` For example, aconventional diode., de-. modulator circuit 78, as shown in FIG. 9, mayboem-- ployed -for this purpose. It is only necessary to connect Forexample, as-` sume that the signals generated in the windings 65Athrough 65D are positive at the ends thereof indicated. by the dots. Inthis condition a positive signal is applied coupled to the demodulator.

thearmatu 12 :to powerfinput terminals 80 and the tachometer 65 tothe'cont'rlinput terminals 82. The

output terminals 20 may beconnected to the center tap 84 of thetransformer 85 and to ground. 1

Another embodiment of the present invention is disclosed in FIG. 7wherein a three-phase alternator 90 is coupled Yto the prime mover 16and includes a iield Wind` ing 92 and a three-phase armature 94. Atachometer 96 having a three-phase winding is connected to the shaft ofthe prime mover 16 to'provide a three-phase control signal. Threeseparate demodulatorsf98, 99 and 100 are coupled to the individualphases of the armature 94 for demodulatng fthe armature output toprovide alternating current output signalspacross output terminals 102,106 and 104. The demodnlators 98, `99 and 100 include control inputterminals 105, y106 and 107 respectively, which are coupled torespective windings of the tachonteter 96, as shown, so that fthecontrol signals applied tok any demoduilator are in phase with thearmature output The'demodulators 98-100 may be of any conventional typesuch as the demodulator 62 shown in FIG. .5 or the demod-ulator ,78shown in FIG. 7. Of course if fthe demodulator 62 isemployed additionalwindings will be required `as illustrated in FIG. 5. The output signalsfrom the demodulators V98-100 may be connected tor separate loads or maybe connected to a common loadviby connecting the outputs in parallel.Where the demodulators are connected to a common load the ripplecomponent in the output is materially reduced due to the ripple voltagecomponents in each of the demodulators being 120 out of phase with theripple voltage components yin the outputs of the other demodulators.

A three-phasef output signal may be obtained by employing a three-phasealternator having three separate magnetic circuits for the respectivephases of the alter nator and providing a separate field winding foreach of the three phases. To control the magnetic fields produced by thefield windings, a three-phase reference signal may be employed with theindividual phasesv of the reference signal being coupled to respectivefield windings.

The generator employed inthe apparatus of this in? vcntion may -beeither 4a rotating or -a Statie-naryV armature type 4and it may have anydesi-red number of poles. FIG. 8 is a simpliiied illustration of thefield windings of a six-pole machine. connected in series across'theoutput of the reference signal generator 18. Thus .the magnetic fieldproduced by any two adjacent poles is controlled in -amplitude anddirection in accor-dance with the signal produced by the generator 18.

From the various embodiments of the invention which have beenillustrated, it will be apparent that many types of circuits may beemployed in carrying out the present invention. Various types ofdemodulating means such as the commutator arrangement disclosed in FIGS.2 and 4 may -be employed for demodulating the armature output of agenerator and where an electronic demodulator is employed such as thetransistor demodulator 62 shown in FIG. 5 or the diode demodulatordisclosed in FIG. 9, various types of control signal generators may beemployed for generating a control signal having the frequency of themodulated signal produced in the armature out-put. Also various types ofreference signal generators may be employed to generate an alternatingcurrent modulating signal. It is of course not necessary that thismodulating sign-al he a sinusoidal wave; it may be a square wave or anyother type of alternating current Wave depending upon the desired outputsignal Waveform.

What is claimed is:

1.V Apparatus for producing alternating current comprising a generatorhaving an armature for producing an alternating current output and atleast one eld winding for.v producing amagnetc .field'for the armature,means vfor driving the generator, means for applying an alter-l natingcur-rent signal having a predetenmined frequency tothe field winding tocause the armature to produce an alternating current output "having |awave .form which is a combination of -aiirst` component frequency equalto the predetermined frequencyA andta 'second componentfrequencypropofrtional to the speed of thejdriving means,r a pair. ofoutput terminals and electronic switching means coupled between thearmature and the output terminals and under the control of the, drivingmeans yfor alternately switching the output from the armature to producean alternating current output signal across kthe output terminals whichchanges in polarity at twice the rst component frequency.'

2. Apparatus for producing alternating current comprising an alternatorhaving anarmature and at least one field winding for producing amagnetic field for the armature, means for driving thealternator, meansfor applying an alternating current reference signal fto the eld windingto cause the armature tol produce an alternating current output in theform of a modulated wave wherein the frequency of the modulated wave isproportional lto the speed of the drivingr means and thefrequency of themodulating wave is equalto the frequency of the reference signal, a pairof output terminals, a demodulator connected between` the armature andthe output terminals, means coupled to the alternator for generating anyalternating current control signal having a frequency equal to thefrequency Vof the modulated wave and means for coupling said last namedmeans to the demodulator.

3. An apparatus as dened in claim 2 wherein the de modulator is a phasesensitive full wave transistor demlodand the armature, means forapplying an alternating cur- As shown, the adjacent poles are rentsignal having the predetermined frequency tot-he field windings tocontrol the magnitude and direction of a magnetic field produced byadjacent poles and thereby control the amplitude and phase of thearmature output in accordance with the signal applied to the fieldwindings to pro'- vide `an armature output in the form of a modulatedwave which changes phase during each half cycle of the modulating wave,wherein the frequency of the modulated wave is proportional to the speedof rotation of the armature and the frequency of the modulating wave isequal to the predetermined frequency, a pair of output terminals,electronic demodulating means coupled between the armature and theoutput terminals and electrical signal generating means coupled to thedemodulating means and responsive to the speed of rotation of thearmature for controlling the operation of the demodulatiug means.

5 An apparatus as defined in claim 4 wherein the armature includes athree-phase winding and the demodulating means for demodulating thearmature output includes a demodnlator individually coupled to each ofthe phases of the armature.

6. An apparatus as defined in claim 5 wherein the electrical signalgenerating means is a tachometer having three windings, one winding ofthe tachometer being coupled to each of the demodulators connected tothe armature.

7. Apparatus for producing alternating current comprising a generatorhaving an armature and at least one field winding for producing amagnetic field for the armature, means for driving the generator toproduce rotary motion between the field windings and the armature,

means fior applying'an alternating current referencesigv'nale-to?thelii'elidi Winding to cause the armature to produceanaalternating'- current output inthe form of a modul-ated"wavefwhereinftl-ie frequency of the modulated Wave is proportionaltothespeed ofthe driving means and the Vfrequency 'of themodulatingv Wave isequal to thefrequency ofthe reference signal,- electronicphase-,sensitive demodulator meanehavingpower input terminals,- controlV input' `'tenninalsl-andvou'tpfut terminals for supplying power toal'lfoad; meansfor connecting the-power input terminals to thearmature', electrical signalgenerating means couplede tofthe generatorfor.. producing an` electrical sign-al Y havinga frequency equal tothe'frequency of the. reference signal and means for connecting theelectrical sig.-v

nali generator to the controli inputE terminals. of the demodwla-torVmeans; foncontrollifng the. operation of the( demodulatorfmeans to.produce la: signal. across the output. terminals havingl a frequencyequal; tof-the; frequency ofl the `reference signal.

8v. Ain apparatus as output;1 tenniualsofthedemodulubor means.1A

. 9;.An1apparatusasdefined. inrclaim 7' wherein the electrical` signal:`generator, is, a tachometer coupled to the driving means.. Y

ILO.: Anl apparatus,asdefinedI in. claim 9fwherein the,

armature, includes a, polyph'ase winding, wherein the demodulator meansyincludes; la separate single phase demodulator lconnected betweeneachfphlasreof the armature and the output tern-iinals, and; wherein thetachometer includes a polyphase winding,

defined; claimv 7 wherein the. demodulator' means: includes;`aplurality; of' semi-condito tou:- devi'ces. connected', inseries,Ibetween theinputl and 11. An yapparatus for producing alternatingcurrent having a controlled; frequencvcomprisi-ng an'a1ternato1-f`having laY three phase armature iffor producing an alter,-y natingcurrent output yand. atleast one field Windinggfor` producing aymagnetic fieldr 'for the, a,rinature,l means` for driving the;alternator to produce rotary motion between the armamre andtheeldfwinding, means forY applyinganalternating currentvreerence signaltothe eldwinding to cause: ,the armature. to .produce an alternatingcunrent:

output 2in the Iiiornr ofga'suppressed. carrier modulated.

lating the varmature output to produce an output signal" f having `afrequency equal to thereference signal, and' means for connecting theVoutputs of the 'demodulatois to provide a three phase outputv signal; A1

References Cited in thefle 'of this patent i vUNITED STATES PATENTS*783,708* stanley Feb. 2s, 190s 2,528,111 Buckunl 011,31, 195o o2,695,371 Barnesvr Nov. 23, 1954:-

2,854,617 Johnson Sept. 30,- 195,8;

